1. Field of the Invention
The present invention relates to boosting transformers used in high-frequency heating devices.
2. Description of the Background Art
Conventional Art
Conventionally, high-frequency heating devices such as microwave ovens have used a boosting transformer configured as shown in FIG. 19. Such conventional transformer first of all has a winding including a primary winding 20 and a secondary winding 21 and a filament winding 23. These windings are coupled together via a magnetic circuit formed of a magnetic body in the form of two ferrite cores 24. As shown in the FIG. 19 cross section, windings 20, 21, 23 are each arranged in the direction of the height of the boosting transformer, i.e., the lateral direction in the figure. Primary winding 20 has a width in the direction of the height of the boosting transformer W1 and a thickness as measured when the winding is stacked T1, wherein width W1.gtoreq.thickness T1, and secondary winding 21 also has a similar width-thickness relationship.
As such, the boosting transformer is sized to have a height large relative to its width and depth. This has been a limitation in determining where such boosting transformer should be attached in a high-frequency heating device which is complicated and has a high voltage line arranged therein and also has a complicated internal structure.
If the secondary winding has an insufficiently divided width, a problem will occur as described below: normally, the secondary winding receives a high voltage, which is, between the top and end of the winding, an instant, maximal voltage of 6 kv to 10 kv. As shown in FIG. 21, secondary winding 21 is successively wound around an insulation member 25 in the direction of the arrow and thus successively stacked, and it completes when it reaches a winding count as defined. If secondary winding 21 is provided as described above, however, secondary winding 21 provided through such process will inevitably have a portion failing to align and thus displaced.
In providing a secondary winding, as described above, the winding is labeled V0 at its top, V1, V2, . . . at its return points and V9 at its end, as shown in FIG. 21. As such, if the secondary winding is provided in alignment, the winding normally has the V9 position adjacent to the V7 position. However, if at the ending, V9 position the winding is displaced down from its appropriate layer level, the displaced winding will be processed adjacent to the winding positioned at V5 or V3. If a winding have such displacement, in proportion to the number of such displacements the winding will receive a voltage twice to triple a voltage which a winding provided in alignment would receive.
Conventionally, a secondary winding has been divided normally into two to three blocks to reduce its width W to prevent any significant displacement thereof and thus reduce a voltage that would otherwise be applied.
In a boosting transformer, each winding and a magnetic body must be insulated from each other. To achieve such insulation, insulation members 25, 26 are provided as shown in FIG. 19. Insulation member 25 is structured to provide a plurality of protruding, dividing walls surrounding primary winding 20, secondary winding 21 and filament winding 23 to insulate such windings from each other and also divide the high-voltage generating, secondary winding normally into two to three blocks, as described above (in FIG. 19, three blocks). Insulation member 25 thus structured results in the transformer having an increased height. Insulation member 26 insulates windings 20, 21, 23 and core 24 from each other.
Furthermore, in providing the aforementioned magnetic circuit to provide a permeability adjusted to match the circuit's operating state, insulation members 25, 26 are structured to allow ferrite core 24 to have a gap 22. As a result, when the boosting transformer operates a magnetic flux varies and ferrite core 24 thus oscillates and produces a noise. Accordingly, to prevent such noise a core fixing band 27 or an adhesive or the like must be used to fix ferrite core 24 to reduce the noise. This degrades the workability and reliability of the transformer and increases the cost for the same.
Furthermore, conventionally a boosting transformer is assembled through a procedure as shown in FIG. 20, having the following steps:
in a first step, primary winding 20, secondary winding 21 and filament winding 23 are successively wound around insulation member 25;
in a second step, insulation member 26 is attached to insulation member 25;
in a third step, two cores 24 are inserted into the combination of insulation members 25 and 26;
in a fourth step, core fixing band 27 is attached to fix ferrite core 24; and
in a fifth step, the above is soldered to a temporarily fixed terminal to complete a boosting transformer.
Since such assembling procedure is taken, to produce a boosting transformer each winding must be wound around an insulation member or it could not have a magnetic material attached thereto. As such, in its production the boosting transformer must be processed through a carefully considered procedure and it is thus produced inefficiently